The present invention relates to a magnetic head, a fabrication method therefor, and a magnetic storage device. More specifically, the present invention relates to a magnet head for recording or reproduction with respect to a perpendicular magnetic storage medium, which is used mainly in applications such as a hard disk drive (HDD), together with a method of fabrication thereof and a magnetic storage device.
The densities achieved by magnetic recording/reproduction devices such as hard disk drives are rapidly increasing, and 40 to 100 Gbpsi (gigabits/inch2) is becoming the next target for a real storage densities. Any attempt to achieve such storage densities by using a conventional in-plane recording method (longitudinal recording method) will make it highly likely that the magnetically recorded data will be destroyed by thermal effects, due to a problem called thermal instability. That is why perpendicular recording methods are considered to be advantageous.
The resistance of a medium to thermal instability is proportional to the product of its magnetic energy Ku per unit volume and the volume V of particles. To increase the linear storage density with an in-plane recording method, it is necessary to reduce the film thickness of the medium in order to reduce the diamagnetic flux of the magnetized medium. This reduces the volume V, which reduces the thermal instability resistance. The magnetic energy Ku per unit volume could be increased in order to prevent this, but that would increase the antimagnetic power, making recording difficult.
With a perpendicular recording method, on the other hand, the direction of magnetism is in the thickness direction of the medium, so that it is not necessary to reduce the film thickness of the medium and thus there can be a favorable thermal instability resistance even with a comparatively small value of Ku, making it easy to achieve a higher density.
However, to achieve an even higher surface density with the perpendicular recording method, it is necessary to increase Ku anyway. Studies performed by the present inventors have proved that there are structural problems with prior-art recording heads, relating to the fabrication of a recording head that can obtain a large flux in a stable manner. This problem is described in detail below.
A schematic view showing a section through the structure of a prior-art perpendicular recording/reproduction magnetic head is shown in FIG. 12. In this figure, a magnetic head 100A for recording and a magnetic head 100B for reproduction are shown in a state in which they are positioned above a medium 200.
The recording head 100A has a configuration such that an annular magnetic path is formed by a main magnetic pole 111, an auxiliary magnetic pole 112, a return yoke 113, and a soft-magnetic underlayer film 216 that is provided on the storage medium 200, and a recording coil 114A is provided so as to intersect this magnetic path.
Similarly, the reproduction head 100B has a configuration such that an annular magnetic path is formed by a main magnetic pole 111, an auxiliary magnetic pole 112, a return yoke 113, and the soft-magnetic underlayer film 216 provided on the storage medium 200,and a reproduction coil 114B is provided so as to intersect this magnetic path.
The return yoke 113 of the recording head 100A is formed of a soft magnetic film that is superimposed on top of a substrate S. The return yoke 113 of the reproduction head 100B, on the other hand, is formed of a substrate S which is itself formed of a soft magnetic material.
A lubrication film 117 of a substance such as diamond-like carbon (DLC) is provided on a medium-facing surface 118 that faces the medium 200.
In the recording head 100A, a current passing through the recording coil 114A causes a large amount of magnetic flux to be generated by the comparatively thick auxiliary magnetic pole 112. This is concentrated in the main magnetic pole 111 so that a large flux escapes to the medium 200 to magnetize a perpendicular recording layer 215 and thus record information. Note that a bias layer 218 is provided in the medium 200.
In the reproduction head 100B, reproduction is done by detecting an induction current that is generated in the reproduction coil 114B provided so as to cross the annular magnetic path.
To ensure that a sufficiently large amount of flux is supplied to the main magnetic pole 111 in the recording head 100A, it is necessary to make the auxiliary magnetic pole 112 thicker than the main magnetic pole 111. If the distance from the medium 200 to the auxiliary magnetic pole 112 is made to be substantially the same as the distance from the medium to the main magnetic pole 111, it becomes difficult for the magnetic flux to concentrate in the main magnetic pole 111 and it also becomes impossible for a large amount of flux to escape. For that reason, it is necessary to arrange the auxiliary magnetic pole 112 in a state in which it is recessed (offset) by a very small amount (indicated by reference letter L in the figure) from the surface that faces the medium 200.
It is also necessary to recess the return yoke 113with respect to the medium-facing surface, to ensure that nothing is recorded on the medium due to flux concentrations at corner portions thereof.
In contrast thereto, the protruding part of the main magnetic pole 111 is formed to be narrow so that flux is concentrated therein, and thus it has a high magnetic resistance. Since a large amount of magnetic flux flows within the main magnetic pole 111 and thus a large amount of flux escapes from the tip thereof, it is necessary to make the protruding part of the main magnetic pole 111 as short as possible to reduce its magnetic resistance. In other words, the auxiliary magnetic pole 112 and the return yoke 113 ought to be as close to the medium 200 as possible, while still being recessed therefrom. Of course, the closer that the recording coil 114A is to the perpendicular recording layer 215, the larger is the flux that is generated at the tip of the main magnetic pole 111.
To summarize the above discussion: to increase the magnetic strength for recording with respect to the medium, it is necessary to place all of the auxiliary magnetic pole 112, the return yoke 113, and the recording coil 114A as close as possible to the medium 200, while ensuring that they are recessed by an extremely small amount from the main magnetic pole 111. The situation of the reproduction head 100B is similar.
With the prior-art perpendicular magnetic heads 100A and 100B exemplified in FIG. 12, however, structural constraints make it difficult to fabricate a stable assembly that satisfies these requirements in a satisfactory manner.
The description now turns to a simplified version of the process of fabricating the magnetic head 100A for recording.
The return yoke 113, the recording coil 114A, the main magnetic pole 111, and the auxiliary magnetic pole 112 are deposited and patterned in that order on a substrate S. The resultant stack of film layers is then sliced in a direction perpendicular to the film surface and the cut surface is lapped to form the medium-facing surface 118. Finally, the DLC lubrication film 117 is formed to complete the recording head 100A.
However, errors in the lapping step during the formation of the medium-facing surface 118 are on the order of ±0.15 μm. This means that, if the aim is to recess the edge positions of surface of the auxiliary magnetic pole 112 that faces the medium 200 by an average of 0.15 μm, where this auxiliary magnetic pole 112 requires more accurate control, this recess could end up as being 0.3 μm in the worst case. If that happens, the flux strength generated from the main magnetic pole 111 is degraded to approximately 70% in comparison with an assembly with a recess of only 0.15 μm.
Furthermore, all of the return yoke 113, the recording coil 114A, the main magnetic pole 111, and the auxiliary magnetic pole 112 are formed by photolithography, combinations of patterning errors (±0.1 μm) and alignment errors (±0.2 μm) could lead to variations of the edge positions that are on the order of ±0.3 μm. If the lapping shaves off 0.15 μm in excess and the worst case is assumed, the position of the edges of the return yoke 113 will have to be recessed by approximately 0.9 μm to ensure that the return yoke 113 does not protrude into the medium-facing surface 118. In such a case, the recording flux strength will decay further, to approximately 90%. Similarly, if the recording coil 114A is displaced in the direction away from the medium 200, the generated flux strength will decay further to approximately 80%.
If it is assumed that all of these errors occur in the worst-case direction, the total error will end up as 0.7×0.9×0.8=0.5, halving the recording flux strength. In principle, the perpendicular magnetic recording method has the advantage of resistance to thermal instability, but a drop in the recording flux strength would make it more likely for data to be lost due to thermal effects, so that this advantage is lost in practice.